May 16, 2006
Lactic Acid Is Not Muscles' Foe, It's Fuel
By GINA KOLATA Everyone who has even thought about exercising has heard the warnings about lactic acid. It builds up in your muscles. It is what makes your muscles burn. Its buildup is what makes your muscles tire and give out.
Coaches and personal trainers tell athletes and exercisers that they have to learn to work out at just below their "lactic threshold," that point of diminishing returns when lactic acid starts to accumulate. Some athletes even have blood tests to find their personal lactic thresholds.
But that, it turns out, is all wrong. Lactic acid is actually a fuel, not a caustic waste product. Muscles make it deliberately, producing it from glucose, and they burn it to obtain energy. The reason trained athletes can perform so hard and so long is because their intense training causes their muscles to adapt so they more readily and efficiently absorb lactic acid.
The notion that lactic acid was bad took hold more than a century ago, said George A. Brooks, a professor in the department of integrative biology at the University of California, Berkeley. It stuck because it seemed to make so much sense.
"It's one of the classic mistakes in the history of science," Dr. Brooks said.
Its origins lie in a study by a Nobel laureate, Otto Meyerhof, who in the early years of the 20th century cut a frog in half and put its bottom half in a jar. The frog's muscles had no circulation - no source of oxygen or energy.
Dr. Myerhoff gave the frog's leg electric shocks to make the muscles contract, but after a few twitches, the muscles stopped moving. Then, when Dr. Myerhoff examined the muscles, he discovered that they were bathed in lactic acid.
A theory was born. Lack of oxygen to muscles leads to lactic acid, leads to fatigue.
Athletes were told that they should spend most of their effort exercising aerobically, using glucose as a fuel. If they tried to spend too much time exercising harder, in the anaerobic zone, they were told, they would pay a price, that lactic acid would accumulate in the muscles, forcing them to stop.
Few scientists questioned this view, Dr. Brooks said. But, he said, he became interested in it in the 1960's, when he was running track at Queens College and his coach told him that his performance was limited by a buildup of lactic acid.
When he graduated and began working on a Ph.D. in exercise physiology, he decided to study the lactic acid hypothesis for his dissertation.
"I gave rats radioactive lactic acid, and I found that they burned it faster than anything else I could give them," Dr. Brooks said.
It looked as if lactic acid was there for a reason. It was a source of energy.
Dr. Brooks said he published the finding in the late 70's. Other researchers challenged him at meetings and in print.
"I had huge fights, I had terrible trouble getting my grants funded, I had my papers rejected," Dr. Brooks recalled. But he soldiered on, conducting more elaborate studies with rats and, years later, moving on to humans. Every time, with every study, his results were consistent with his radical idea.
Eventually, other researchers confirmed the work. And gradually, the thinking among exercise physiologists began to change.
"The evidence has continued to mount," said L. Bruce Gladden, a professor of health and human performance at Auburn University. "It became clear that it is not so simple as to say, Lactic acid is a bad thing and it causes fatigue."
As for the idea that lactic acid causes muscle soreness, Dr. Gladden said, that never made sense.
"Lactic acid will be gone from your muscles within an hour of exercise," he said. "You get sore one to three days later. The time frame is not consistent, and the mechanisms have not been found."
The understanding now is that muscle cells convert glucose or glycogen to lactic acid. The lactic acid is taken up and used as a fuel by mitochondria, the energy factories in muscle cells.
Mitochondria even have a special transporter protein to move the substance into them, Dr. Brooks found. Intense training makes a difference, he said, because it can make double the mitochondrial mass.
It is clear that the old lactic acid theory cannot explain what is happening to muscles, Dr. Brooks and others said.
Yet, Dr. Brooks said, even though coaches often believed in the myth of the lactic acid threshold, they ended up training athletes in the best way possible to increase their mitochondria. "Coaches have understood things the scientists didn't," he said.
Through trial and error, coaches learned that athletic performance improved when athletes worked on endurance, running longer and longer distances, for example.
That, it turns out, increased the mass of their muscle mitochondria, letting them burn more lactic acid and allowing the muscles to work harder and longer.
Just before a race, coaches often tell athletes to train very hard in brief spurts.
That extra stress increases the mitochondria mass even more, Dr. Brooks said, and is the reason for improved performance.
And the scientists?
They took much longer to figure it out.
"They said, 'You're anaerobic, you need more oxygen,' " Dr. Brooks said. "The scientists were stuck in 1920."
First, in the ex phys community, this is well known and has been for quite a few years. However, in the sport community and recreational ones, it's not been discussed. Not that it really matters much as it doesn't impact how people train - it just impacts how they discuss how they train.
1) It's not Lactic Acid that fatigues the muscles. It's an accumulation of hydrogen ions (acid).
2) The reason scientists thought Lactic Acid was the cause of the fatigue is the fact that Lactate (the dissociated acid-free version of Lactic Acid) concentrations in the blood give a good indication of how much acid is actually in the muscle. So when blood lactate is high, that means there's a lot of acid accumulating in the muscle. You can sort of see then how the mistake was made. Lactate is high in the blood. Lactic Acid is high in the muscles. Must be the Lactic Acid that's the problem. Never was. It was the dissociated acid (H+) that was the problem.
3) The dissociated Lacate, instead of being nasty, is used as a fuel (taken up by the muscles and also converted to carbon compounds in the liver that can be used by the muscles for energy).
Interesting stuff, eh?
comment from John Berardi:
Here's a comment I got:
I think it's important to remember that you burn lactate, but H+ accumulation still leads to phsyiological changes that limit performance, specifically blocking the ability of calcium to bind to troponin. This is one of the reasons why the buffer capacity is important, ideally you can have large concentrations of lactate, with minimal changes in hydrogen ion concetration, because you will buffer out the changes in H+.
Acid is still "bad" it's just they're acknowledging the endurance preserving effect of lactate.
If my understanding is correct...
It is correct - good synopsis.
I just read this mainstream treatment (NY Times article) of the topic and while it's good to get the message out, I think the message wasn't as well presented as it could have been.
BTW, the exercise science community has known about this for years although it hasn't reached mainstream consciousness -- probably because people like to see things as black and white.
And in this case we've got lactate (dissociated form) being good, lactic acid (acid form) being bad.
And we've got this rogue something or other called H plus (H+) or, worse yet, the hydrogen ion. Whenever you introduce an element from the periodic table people crap their pants.
So let's just stick with lactic acid making your burn and making you slow. It's less confusing that way.
Thread: Lactic Acid ( the burn )